The subject matter described herein relates to surface inspection techniques, and more particularly to detecting multi-domain states in perpendicular magnetic media.
Advances in magnetic recording media have led to the development of recording media that have a magnetic layer in which the axis of magnetization is perpendicular to the surface plane of the substrate, referred to sometimes as perpendicular magnetic media. Perpendicular magnetic media permit a high areal data density. Perpendicular magnetic media also have a soft magnetic under layer which is beneath the active magnetic layer. The purpose of the soft magnetic under layer is to provide a return path for the magnetic flux. However, the soft magnetic under layer of perpendicular magnetic media tends to be characterized by a low coercive field, and hence can readily fracture into multiple domains. Regions including multiple magnetic domain states cause magnetic noise when attempting to read data from a magnetic medium. Hence, it is desirable to detect regions that include multiple magnetic domain states in perpendicular magnetic recording media.